This application is based on application No. 11-23969 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a near field light emitting element and an optical head which are suited to be employed in a high density optical memory (for recording/reading), a high resolution microscope or an optical processing device.
2. Description of Related Art
In the art of optical memories which optically record and read information, in recent years, with speed-up of computer processing and development of multimedia, high-density devices which are capable of recording an extremely large volume of information are demanded, and in order to comply with the demand, a near field optical recording technique is suggested. In a conventional optical memory using a laser beam, the recording density is limited depending on the diffraction limit of light, and such an optical memory can record and read marks of sizes of at least light wavelength (several hundred nanometers). A recently proposed optical memory which uses near field optics radiates light to a recording medium (optical disk) for recording/reading with the optical head and the recording medium arranged at an interval of only some dozen nanometers. At this time, the optical memory uses a fiber probe with a minuscule aperture smaller than light wavelength and a solid immersion lens. Thereby, in spite of the diffraction limit, it becomes possible to record and read minuscule marks of some dozen nanometers.
Such a near field optical technique is applicable to optical processing techniques for making minuscule patterns beyond the diffraction limit of light and to high resolution microscopes.
In the field of near field optical techniques, optical probes which permit minuscule light spots of a large quantity of light are desired. By adopting a method in which an aperture is made at a tapered end of an optical fiber, the size of the aperture is approximately 100 nm, and only {fraction (1/100)} or less of light can transmit the optical fiber, that is, the quantity of transmitted light is extremely small.
In order to solve this problem, making a tapered hole by anisotropic etching of a silicon substrate has been suggested (U.S. Pat. No. 5,689,480). By adopting this method, it is possible to increase the quantity of transmitted light. In this method, however, the hole is made in a film of monocrystal silicon by anisotropic etching, which is complicated and costs much.
An object of the present invention is to provide a near filed light emitting element and an optical head which can be fabricated in simple processes and use light efficiently.
In order to attain the object, a near field light emitting element according to the present invention comprises an element body; a first light transmitting portion which is provided on an emergent side of the element body; an intermediate film which is provided on an emergent side of the first light transmitting portion; and a second light transmitting portion which is provided on an emergent side of the intermediate film, the second light transmitting portion being smaller in area than the first transmitting portion. As the element body, for example, a solid immersion lens is used. At least one of the light transmitting portions is a minuscule hole made in a film or a minuscule light transmitting portion which is provided in a multi-layered film by alloying materials of the multi-layered film with each other under a high temperature.
According to the present invention, a light beam incident to the near field light emitting element is converged on the first light transmitting portion, and this converged light comes to the second light transmitting portion via the intermediate film. At the second light transmitting portion, the light beam is further narrowed and is emergent as near field light (in other words, optical near field). The light transmittance of the near field light is higher than the light transmittance when a conventional single slit is used and is almost equal to or higher than the light transmittance when a tapered slit is used.
Further, the first and second light transmitting portions and the intermediate film of the near field light emitting element can be formed by a conventional thin film forming technique and a conventional etching technique, which are easier than the method wherein a monocrystal silicon film is subjected to anisotropic etching.
Further, in the near field light emitting element according to the present invention, preferably, the first and second light transmitting portions are slits which extend in parallel to each other. In this case, the width of the second light transmitting portion (slit) is smaller than the width of the first light transmitting portion (slit). Although desired transmittance can be obtained merely with this arrangement, the transmittance can be further improved by making the direction of polarization of incident light correspond to the extending direction of the slits.